DNA‐Mediated Assembly of Boron Nitride Nanotubes

The dispersion of nanomaterials in solutions is of primary importance for the improvement of their processability, but it also provides a way to investigate phase behavior and to assemble nanostructures in solvents. Several methods based on different interactions have been developed to disperse carbon nanotubes, whereas little development has been made for their boron nitride nanotube (BNNT) counterparts. A direct way to obtain long‐range ordering may be through spontaneous nematic ordering in solutions at sufficiently high concentrations of the nanomaterial fraction. Lyotropic nematics have been observed in various organic and inorganic systems. In this work, the strong interactions between DNA and BNNTs were exploited to fabricate high‐concentration BNNTs aqueous solutions by a simple method, and then, for the first time, nematic ordered ensembles of BNNTs were obtained by filtration. It is proposed that a localized liquid‐crystal phase appears during filtration, as the ordering trend for the BNNTs was found to depend on the concentration of the aqueous solutions of the BNNTs. Moreover, BNNTs were successfully localized on a predefined area by using a thiol‐modified DNA–BNNT hybrid.     

Metal complexes in the catalytic transformations of olefins. 5. Catalytic synthesis of C9-C24 olefins from propylene

The optimum conditions for the production of C₉-C₂₄ olefins with yields of 20–25% (remainder hexenes) by oligomerization of liquid propylene at the Ni(PPh₃)_n (n=2–4)—Et₃Al₂Cl₃ catalytic system were determined by simplex design of experiments. It was shown that the obtained hexenes undergo secondary di- and trimerization reactions.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1299–1303, June, 1992.     

A novel family of layered bismuth compounds II: the crystal structures of Pb0.6Bi1.4Rb0.6O2Z2, Z=Cl, Br, and I

Using various synthetic approaches, we have prepared over 50 new multinary bismuth oxyhalides which crystallize in four layered structure types. Most of the compounds belong to the three previously reported structure types involving fluorite- and CsCl-like metal-oxygen vs. metal-halogen layers as well as single or double halide ion sheets. The majority of Bi_2−xA_xQ_0.6O₂Z₂ (A=Li, Na, K, Ca, Sr, Ba, Pb; Q=Rb, Cs; Z=Cl, Br, I) compounds crystallize in the tetragonal structure of Pb_0.6Bi_1.4Cs_0.6O₂Cl₂ (Y2) while both Bi_1.4Ba_0.6Q_0.6O₂I₂ (Q=Rb, Cs) oxyiodides adopt its orthorhombically distorted, partially ordered version. Due to the lower degree of substitution, the fluorite-like layers in the Y2 structure accommodate more A cations than previously known for related Bi compounds. However, very large Tl⁺ or Rb⁺ give compounds with another, as yet unknown, structure. We discuss the influence of size and charge of A cations and stoichiometry of [Bi_2−xA_xO₂] fluorite layers on structure and stability of layered oxyhalides of bismuth. Also, we predict formation of isostructural compounds with smaller Q cations like Tl⁺ and K⁺.     

1,1′,2,2′,6,6′-Hexaphenyl-4,4′-bipyridinium cation radical

Aniline reacts with 2,2,6,6-tetraphenyl-4,4-bipyrilium perchlorate to form 1,1,2,2,6,6-hexaphenyl-4,4-bipyridine perchlorate. A relatively stable cation radical is formed in the first stage of electrochemical reduction of this compound, which has been examined by ESR, where there are splittings from two nitrogen nuclei and the four protons in the 3,3,5,5 positions: a_N=0.38; a_H=0.14 mT.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 61–64, January–February 1992.     

Multi-walled BN nanotubes synthesized by carbon-free method

Pure multi-walled BN nanotubes were synthesized via a carbon-free chemical vapor deposition process using boron and gallium oxide mixture as reaction precursor. Transmission electron microscopy was used to investigate their structure, morphology and defects. The wall deformation, dependent on tube diameter, was observed and explained in terms of strain relaxation of bond rotation. Opposed to carbon nanotubes, bending of BN nanotubes typically results in fracture at their concave side. Ring defect-related mechanism was proposed to interpret the fracture. The ring defects also result in the formation of a nanocone with 300° disclination. The nanocones end up with BN nanotubes exhibiting the small innermost shell ∼0.4 nm in diameter.     

Study of nucleation and growth in the organometallic synthesis of magnetic alloy nanocrystals: the role of nucleation rate in size control of CoPt3 nanocrystals

High quality CoPt(3) nanocrystals were synthesized via simultaneous reduction of platinum acetylacetonate and thermodecomposition of cobalt carbonyl in the presence of 1-adamantanecarboxylic acid and hexadecylamine as stabilizing agents. The high flexibility and reproducibility of the synthesis allows us to consider CoPt(3) nanocrystals as a model system for the hot organometallic synthesis of metal nanoparticles. Different experimental conditions (reaction temperature, concentration of stabilizing agents, ratio between cobalt and platinum precursors, etc.) have been investigated to reveal the processes governing the formation of the metal alloy nanocrystals. It was found that CoPt(3) nanocrystals nucleate and grow up to their final size at an early stage of the synthesis with no Ostwald ripening observed upon further heating. In this case, the nanocrystal size can be controlled only via proper balance between the rates for nucleation and for growth from the molecular precursors. Thus, the size of CoPt(3) nanocrystals can be precisely tuned from approximately 3 nm up to approximately 18 nm in a predictable and reproducible way. The mechanism of homogeneous nucleation, evolution of the nanocrystal ensemble in the absence of Ostwald ripening, nanocrystal faceting, and size-dependent magnetic properties are investigated and discussed on the example of CoPt(3) magnetic alloy nanocrystals. The developed approach was found to be applicable to other systems, e.g., FePt and CoPd(2) magnetic alloy nanocrystals.     

Direct Bioelectrocatalysis of PQQ‐Dependent Glucose Dehydrogenase

The direct bioelectrocatalysis was demonstrated for pyrroloquinoline quinone‐dependent glucose dehydrogenase (PQQ‐dependent GDH) covalently attached to single‐walled carbon nanotubes (SWNTs). The homogeneous ink‐like SWNT suspension was used for both creating the SWNT network on the microelectrode carbon surface and for enzyme immobilization. Functionalization of the SWNT surface by forming active ester groups was found to considerably enhance SWNT solubility in water with a range from 0.1 to 1.0 mg/mL. The PQQ‐dependent GDH immobilized on the surface of the SWNTs exhibited fast heterogeneous electron transfer with a rate constant of 3.6 s^?1. Moreover, the immobilized PQQ‐dependent GDH retained its enzymatic activity for glucose oxidation. A fusion of PQQ‐dependent GDH with SWNTs has a great potential for the development of low‐cost and reagentless glucose sensors and biofuel cells.     

On bending of a convex surface to a convex surface with prescribed spherical image

We prove the following theorem. LetF be a regular convex surface homeomorphic to the disk. Suppose the Gaussian curvature ofF is positive and the geodesic curvature of its boundary is positive as well. LetG be a convex domain on the unit sphere bounded by a smooth curve and strictly contained in a hemisphere. LetP be an arbitrary point on the boundary ofF andP ^* be an arbitrary point on the boundary ofG. If the area ofG is equal to the integral curvature of the surfaceF, then there exists a continuous bending of the surfaceF to a convex surfaceF such that the spherical image ofF coincides withG andP ^* is the image of the point inF corresponding to the pointP F under the isometry.Translated fromMatematicheskie Zametki, Vol. 58, No. 2, pp. 295–300, August, 1995.     

Glauber Dynamics in the Continuum via Generating Functionals Evolution

We construct the time evolution for states of Glauber dynamics for a spatial infinite particle system in terms of generating functionals. This is carried out by an Ovsjannikov-type result in a scale of Banach spaces, leading to a local (in time) solution which, under certain initial conditions, might be extended to a global one. An application of this approach to Vlasov-type scaling in terms of generating functionals is considered as well.